Population Dynamics Of Small Mammals Research Articles

Influence of temporal variation and seasonality on population dynamics of three sympatric rodents

Population dynamics of small mammals can be strongly influenced by seasonality. Long-term studies are important in detecting population size variation in small mammals, and understanding the causes of that variation. We performed a six-year study to investigate fluctuations in population parameters (reproduction, recruitment, survival rates, abundance, and capture probability) of three rodent species at the core of the Brazilian cerrado domain. Small mammals were captured monthly within two grids during six years at Aguas Emendadas Ecological Station in the Federal District, Brazil. Model selection for explaining variation in rodent survival rates and capture probability was performed using MARK (Robust Design model). All three rodent species showed highest proportion of reproductive females in wet seasons. Calomys tener and T. lasiotis are seasonal and population size is higher in dry than in wet seasons, while the most abundant N. lasiurus had no seasonal patterns. Annual variation in abundance was also important for these three species. Thalpomys lasiotis declined over the six years of the study. These species showed highest survival estimates in the dry season. Our results reinforce the idea that not only climatic (rainfall and drought) events are linked to population numbers, survival rates, and capturability, but also that the life histories of the species can play an important role in their responses to variations in rainfall-productivity events.

Effects of Brush Piles on Small Mammal Abundance and Survival in Central Pennsylvania

Abstract Brush piles have long been promoted as a means to enhance wildlife habitat, yet few studies have experimentally tested the perceived benefits of these structures for wildlife or evaluated the efficacy of different arrangements of these piles within landscapes. During summers 2005 and 2006, we used a mark–recapture study to compare small mammal abundance and survival in forested habitats provisioned with brush piles vs. similar habitats without, both at sites located adjacent to agricultural edges and within the interior of forests in central Pennsylvania. Northern short-tailed shrews Blarina brevicauda, mice Peromyscus, and eastern chipmunks Tamias striatus were all frequently captured within brush piles at edge and interior sites. Peromyscus were significantly more abundant at edge vs. interior sites. The presence of brush piles, however, seemed to have little effect on small mammal abundance or survival with the only potential effect being an increased overwinter survival rate experienced by Peromyscus at brush pile sites. We hypothesize that although brush piles provide cover and foraging sites for small mammals, the large quantities of coarse woody debris that exist naturally in many forested systems may already adequately provide these habitat features, minimizing the effects of brush piles on small mammal population dynamics.

Seasonal demography of a cyclic lemming population in the Canadian Arctic.

1. The causes of cyclical fluctuations in animal populations remain a controversial topic in ecology. Food limitation and predation are two leading hypotheses to explain small mammal population dynamics in northern environments. We documented the seasonal timing of the decline phases and demographic parameters (survival and reproduction) associated with population changes in lemmings, allowing us to evaluate some predictions from these two hypotheses. 2. We studied the demography of brown lemmings (Lemmus trimucronatus), a species showing 3- to 4-year population cycles in the Canadian Arctic, by combining capture-mark-recapture analysis of summer live-trapping with monitoring of winter nests over a 10-year period. We also examined the effects of some weather variables on survival. 3. We found that population declines after a peak occurred between the summer and winter period and not during the winter. During the summer, population growth was driven by change in survival, but not in fecundity or proportion of juveniles, whereas in winter population growth was driven by changes in late summer and winter reproduction. 4. We did not find evidence for direct density dependence on summer demographic parameters, though our analysis was constrained by the paucity of data during the low phase. Body mass, however, was highest in peak years. 5. Weather effects were detected only in early summer when lemming survival was positively related to snow depth at the onset of melt but negatively related to rainfall. 6. Our results show that high mortality causes population declines of lemmings during summer and fall, which suggests that predation is sufficient to cause population crashes, whereas high winter fecundity is the primary factor leading to population irruptions. The positive association between snow depth and early summer survival may be due to the protective cover offered by snow against predators. It is still unclear why reproduction remains low during the low phase.

Influence of Snow, Food, and Rock Cover on Royle’s Pika Abundance in Western Himalaya

Knowledge on demographic responses to environmental and microhabitat factors are crucial to understand the ecological consequences of climate change predictions for species that live in isolated mountainous habitat, such as the Royle’s pika. We examined the influence of snow attributes, food availability, and rock cover on adult and juvenile pika counts and juvenile emergence date based on spatiotemporal variation in these parameters at 10 permanent plots (0.25 ha squares) along an attitudinal gradient of Kedarnath Wildlife Sanctuary during the predispersal period spanning four years. Pika count and its interannual variability at plots were estimated at 4.06Mean ± 0.21SE and 19.65 ± 1.71% CV respectively. Regression analysis showed that spatiotemporal variation in adult counts was related to the interactive effect of snow-cover period and altitude wherein counts increased with snow-cover period only in lower altitudes (β = 0.26 ± 0.08). Juvenile count was related to spring snow-depth (β = 0.074 ± 0.037). Litter number was typically one. Our results confirm the influence of snow as thermal insulator (to pika and their food plants) on population dynamics of small mammals. We also highlight that adult and juvenile populations might be governed by different factors, invoking further studies on age-stratified assessment of population responses to climate change.

Fire‐mediated niche‐separation between two sympatric small mammal species

AbstractFire is a key ecological process influencing the population dynamics of small mammals. Whilst shifting competitive advantage amongst small mammal species following a single fire event is well‐documented, there has been little investigation of the potential influence of fire frequency on small mammal interspecific interactions. In this study, we investigated the effect of fire frequency on the abundance of two small dasyurid mammals, Antechinus stuartii and A. flavipes, which occur sympatrically in some parts of their range. The two antechinus species are known to have different habitat preferences, so it is possible that fire regimes may promote their coexistence in areas of sympatry by altering vegetation structure. To investigate this possibility, we estimated the abundance of both species using replicate sites which differed in the number of times burnt (1–4) during the last four decades, but with identical time‐since‐fire. Proportionally, we captured greater numbers of A. stuartii in less frequently burnt sites and greater numbers of A. flavipes in more‐frequently burnt sites. Hence, fire may mediate niche‐separation between these two species. To clarify further this pattern of response to fire frequency, we investigated which structural habitat variables differed between fire frequencies, and compared antechinus abundances with structural vegetation characteristics. We found a trend for lower ground cover density under higher fire frequencies. This offers one potential explanation of the patterns of abundance that we observed. Our study provided insights into the complexities of small mammal responses to fire, and strongly suggests that fire could mediate competitive interactions between species.

Conifer seed predation by terrestrial small mammals: A review of the patterns, implications, and limitations of top-down and bottom-up interactions

Conifer seeds are an important component of the diet of many terrestrial small mammals, and seed predation by small mammals is often implicated as a major limiting factor in the recruitment and regeneration processes in coniferous forests. However, studies examining the effects of conifer seed quality and availability on individual small mammals and their populations are scarce. This interaction has important ecological implications at multiple trophic levels in forest ecosystems, given the considerable differences in seed defenses among associated conifer species, the prevalence of mast seeding as a pulsed resource in coniferous forests, and the persistent, cascading effects of seed–small mammal interactions observed in other forest systems. Here, I comprehensively review the patterns, implications, and limitations of the literature on post-dispersal seed predation by terrestrial small mammals (mice and voles of families Cricetidae and Muridae) in coniferous forests. This paper mainly focuses on North American forests, since studies on this topic are predominantly in this region, but relevant examples from Europe and Asia are also provided. I present a summary of the identities and impacts of competing conifer seed predators at both the pre- and post-dispersal stages. I also review the various physical, chemical, and population-level defensive strategies utilized by conifers to limit seed predation, and how the foraging and population dynamics of small mammals are affected by these defenses. Special emphasis is placed on the population responses of terrestrial small mammals to conifer mast seeding, a resource pulse–consumer interaction that can provide critical insights into the effects of resource availability on the regulation of behaviors, populations, and communities. I then discuss the behavioral, morphological, biochemical, and population-level mechanisms that seed predators use to overcome plant- and seed-defenses, focusing primarily on conifer seeds and terrestrial small mammals, but literature on other types of seeds and seed predators are included when relevant. Finally, I describe remaining key limitations and knowledge gaps in the current conifer–small mammal literature, and future research avenues that would broaden our understanding of the top-down and bottom-up interactions between conifer seeds and small mammals at basic, applied, and evolutionary levels.

Intra- and interspecific interactions and environmental factors determine spatial–temporal species assemblages of rodents in arid grasslands

Many factors have been shown to affect species assemblages of a community, but studies using long-term spatial–temporal community data are still lacking. In this study, by using population abundance data of 14 rodent species over 25 years in 21 sampling sites, we investigated the effects of taxonomic relation, density dependency, species interaction and climate variation in determining spatial–temporal species assemblages of rodents in arid grasslands of Inner Mongolia in China. By the use of GAMM analysis, we found that intraspecific interactions were more common and more significant than interspecific interactions. Negative interactions between species of the same genus were more common than negative interactions between species of different genera. Dominant species show negative interactions on less abundant or rare species. Positive interactions often occur within rare or less abundant species. Through cluster analysis, we found species assemblages of rodent communities are well explained by assemblages of environmental variables, and species of same genus tend not to occur together as compared to species of the same family. Our results indicate that resource partitioning through intra- or interspecific competition and environmental filtering by climate and vegetation are important forces in shaping the spatial–temporal community structure and the dynamics of small mammal populations in an arid grassland landscape.

Krebs, C. J.2013. Population Fluctuations in Rodents. University of Chicago Press, Chicago, Illinois, ix + 306 pp. ISBN 978-0-226-01035-9, price (hardbound), $55.00

C. J. Krebs, 2013. Population Fluctuations in Rodents. University of Chicago Press, Chicago, Illinois, ix + 306 pp. ISBN 978-0-226-01035-9, price (hardbound), $55.00. Charles Krebs has been a leader in the study of the population dynamics of small mammals for decades, and this book presents both his analyses of specific hypotheses and syntheses of general patterns. The book summarizes a vast literature and will serve as an admirable introduction to population dynamics for its target audience, advanced undergraduates and graduate students and ecologists outside the field. Krebs makes clear that he is concerned with population fluctuations in general, not just population cycles, but most of the book is devoted to results for arvicoline rodents (lemmings and voles), a group that provides several classic examples of population cycling. Krebs has strong ideas regarding the proper approach to population ecology. As he sees it, there are 2 problems regarding changes in population densities, 1 spatial and 1 temporal. The spatial problem involves shifts in average density of rodents across different habitats, differences that he believes usually reflect different availability of resources, particularly food and cover (protection from predation). The temporal problem, which consumes most of the book, concerns changes in density through time within a habitat, which is the traditional realm of population dynamics. He argues that one should attack the latter problem by finding environmental factors that strongly influence rates of population change and not density per se, a stance that may underemphasize the interaction of environmental factors with density. Krebs provides background in the first 2 chapters by considering different ways to classify population change, including time-series analysis, and geographical shifts in patterns of population dynamics, particularly those that change with latitude. …

Road verges are refuges for small mammal populations in extensively managed Mediterranean landscapes

Understanding how roads affect the persistence of animal populations is one of the challenges of road ecology. Small mammals are of great interest on account of their value as indicators of environmental impacts and their key role in ecosystems. Nevertheless, there is a large gap in our knowledge of small mammal communities in the proximity of roads. An intensive study was conducted of the effect of a motorway on the small mammal communities in an extensively managed Mediterranean landscape. Live-trapping methods were used over a 2-year period to characterise the structure and dynamics of small mammal populations at increasing distances from the motorway (0–500–1000m). In total, 1004 individuals of three species were captured. All three were significantly more abundant nearest to the motorway. In addition, in the case of the wood mouse, a higher proportion of juveniles was found at 0m and 500m from the motorway and its abundance was independent of other, habitat-related, characteristics. The greater abundance of small mammals in close vicinity to the motorway became more obvious during the second year, when a population crash reduced captures by over 60%. Thus, the ratio of captures alongside the motorway relative to those at the other distances analysed rose from approximately 3:2 to 9:2. The results point to roadside verges being an important refuge for small mammals in terms both of greater abundance and population stability. This finding has important implications from the viewpoint of conservation biology and for management of the environmental impacts of roads.

Cyclic voles and shrews and non-cyclic mice in a marginal grassland within European temperate forest

Cyclic population dynamics of small mammals are not restricted to the boreal and arctic zones of Eurasia and North America, but long-term data series from lower latitudes are still less common. We demonstrated here the presence of periodic oscillations in small mammal populations in eastern Poland using 22-year (1986–2007) trapping data from marginal meadow and river valley grasslands located in the extensive temperate woodland of Białowieża Primeval Forest. The two most common species inhabiting meadows and river valleys, root vole Microtus oeconomus and common shrew Sorex araneus, exhibited synchronous periodic changes, characterised by a 3-year time lag as indicated by an autocorrelation function. Moreover, the cycles of these two species were synchronous within both habitats. Population dynamics of the striped field mouse Apodemus agrarius was not cyclic. However, this species regularly reached maximum density 1 year before the synchronized peak of root voles and common shrews, which may suggest the existence of interspecific competition. Dynamics of all three species was dominated by direct density-dependent process, whereas delayed density dependent feedback was significant only in the root vole and common shrew. Climatic factors acting in winter and spring (affecting mainly survival and initial reproduction rates) were more important than those acting in summer and autumn and affected significantly only the common shrew. High temperatures in winter and spring had positive effects on autumn-to-autumn changes in abundance of this species, whereas deep snow in combination with high rainfall in spring negatively affected population increase rates in common shrew.

Global climate change and small mammal populations in north-central Chile

Since 1989 we have monitored small mammal populations at a semiarid site in north-central Chile with a large- scale livetrapping grid complex. Selective exclusions of vertebrate predators or putative small mammal competitors, or both, have yielded relatively small or mostly transitory effects, or both, on small mammal population dynamics and plant community composition. During the study period 5 El Nino-high rainfall episodes have occurred lasting 1-3 years. Resident or core small mammals such as Abrothrix olivaceus, Phyllotis darwini, and Octodon degus experience dramatic fluctuations during and following rainfall pulses. Temporary resident or opportunistic species such as Oligoryzomys longicaudatus and A. longipilis disappear from the thorn scrub for varying periods of time. All species persist in more mesic nearby habitats near dry stream courses (aguadas). Since a 3-year high rainfall event in 2000-2002 mean annual rainfall has increased in this region, mainly due to a lack of prolonged droughts. Under these conditions, and building on a qualitative model proposed by Noy-Meir, long-lived species might become more abundant. Changes in the small mammal assemblage are consistent with these predictions; O. degus, a caviomorph rodent with a long life span, now comprises a more constant proportion of the small mammal biomass in the thorn scrub, and we have documented reduced variation in species diversity. Increased rainfall, a predicted consequence of global climate change in this region, might be leading to changes in small mammal assemblage structure and composition and ultimately will result in a more stable, less oscillatory assemblage in the thorn scrub. Additionally, invasive groups such as introduced lagomorphs and ephemeral plants might become more abundant in this community. The long-term consequences of changes in rainfall patterns due to El Nino Southern Oscillations (ENSOs), with important teleconnections to global-scale phenomena, will lead to diverse changes at the community level here.

Guild composition and habitat use of voles in 2 forest landscapes in south‐eastern Norway

It is widely believed that intensive forestry has influenced small mammal population dynamics, and thereby the entire mammalian community in Fennoscandian boreal forests. The nature of these impacts on the different species is subject to debate. We live-trapped voles between 2006 and 2009 in 2 commercially harvested forests in south-eastern Norway. We investigated the variation in vole abundance among habitat types (e.g. mature forest and clear-cut) and the hypothesis that graminivorous species such as field voles (Microtus agrestis L.) benefit from clear-cuts at the expense of forest dwellers (i.e. the bank vole, Myodes glareolus Schreb.), using fine-scale descriptors of the ground vegetation. We could not find support for the hypothesis that field voles show a preference for clear-cuts, and their overall abundance was low, while bank voles were the dominant species in all habitat types, including clear-cuts in the peak and pre-peak years. We found a positive association between bank vole abundance and bilberry (Vaccinium myrtillus L.) availability rather than a specific habitat type. Low field vole density in clear-cuts might be due to variation in local productivity and ground vegetation as well as to large variation in the species temporal dynamics. The latter is particularly associated with the widespread decline of field voles in Scandinavia. Logging has the potential to negatively affect bank vole population dynamics because of the negative effect on bilberry development.

Effects of predation, fire, and supplemental feeding on populations of two species of Peromyscus mice

Abstract Food resources and predation play important roles in determining small mammal population dynamics. These factors also can interact as individuals under predation pressure make trade-offs between access to food resources and exposure to predators. Fires consume food sources and reduce cover, which increases exposure to predators. For species that occur in areas with frequent fire, it is instructive to consider how all of these factors interact to affect populations of interest. We examined how supplemental feeding, mammalian predator exclusion, and prescribed fire affected survival, abundance, and reproduction of cotton mice (Peromyscus gossypinus) and oldfield mice (P. polionotus) in a longleaf pine ecosystem. Burning and predator exclusion interacted to affect survival of cotton mice; survival was similar in predator exclosures and controls in nonburning periods and in controls following prescribed burns but increased in exclosures following burns. Rates of transitions to reproductive states (wh...

Seed survival on experimental dishes in a central European old‐growth mixed‐species forest – effects of predator guilds, tree masting and small mammal population dynamics

Predation of tree seeds can be a major factor structuring plant communities. We present a three year study on tree seed survival on experimental dishes in an old‐growth forest in central Europe in Austria. We addressed species specific, spatial and temporal aspects of post‐dispersal seed predation. Seeds of Norway spruce Picea abies, European beech Fagus sylvatica, and silver fir Abies alba were exposed on dishes in different types of exclosures which allowed access only to specific guilds of seed predators. Removal experiments were carried out in two old‐growth forests and a managed forest (macro‐sites), including micro‐sites with and without cover of ground vegetation. We conducted the experiment in three consecutive years with a mast year of beech and spruce before the first year of the study. The seed removal experiments were combined with live trapping of small mammals being potential seed predators. Our experiments showed a distinctly different impact of different predator guilds on seed survival on the dishes with highest removal rates of seeds from dishes accessible for small mammals. We observed differing preferences of small mammals for the different tree species. Seed survival in different macro‐ and micro‐habitats were highly variable with lower seed survival in old growth forests. In contrast to our assumption, and in contrast to the satiation hypothesis which assumes higher seed survival in and directly after mast years, seed survival was lower in the year following the mast year of beech when a population peak of small mammals occurred and higher in intermast periods when subsequently small mammal population crashed. This suggests a higher importance of sporadic masting shortly after mast years in intermast periods for establishment of forest trees provided that pollination efficiency is high enough in such years. Combined with the high seed mortality observed after the mast year, this corroborates the important role of seed predation for forest dynamics. An altered synchrony or asynchrony of masting of different tree species and changed masting frequencies through climate change may thus lead to strong and non‐linear effects on forest dynamics.

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

Local spatio-temporal resource variations can strongly influence the population dynamics of small mammals. This is particularly true on islands which are bottom-up driven systems, lacking higher order predators and with high variability in resource subsidies. The influence of resource fluctuations on animal survival may be mediated by individual movement among habitat patches, but simultaneously analysing survival, resource availability and habitat selection requires sophisticated analytical methods. We use a Bayesian multi-state capture-recapture model to estimate survival and movement probabilities of non-native black rats (Rattus rattus) across three habitats seasonally varying in resource availability. We find that survival varies most strongly with temporal rainfall patterns, overwhelming minor spatial variation among habitats. Surprisingly for a generalist forager, movement between habitats was rare, suggesting individuals do not opportunistically respond to spatial resource subsidy variations. Climate is probably the main driver of rodent population dynamics on islands, and even substantial habitat and seasonal spatial subsidies are overwhelmed in magnitude by predictable annual patterns in resource pulses. Marked variation in survival and capture has important implications for the timing of rat control.

Effects of prescribed fire, supplemental feeding, and mammalian predator exclusion on hispid cotton rat populations

Predation and food resources can strongly affect small mammal population dynamics directly by altering vital rates or indirectly by influencing behaviors. Fire may also strongly influence population dynamics of species inhabiting fire-adapted habitats because fire can alter food and cover availability. We used capture-mark-recapture and radio-telemetry studies to experimentally examine how supplemental feeding, mammalian predator exclusion, and prescribed fire affected survival, abundance, and reproduction of hispid cotton rats (Sigmodon hispidus) in southwestern Georgia, USA. Prescribed fire reduced survival, abundance, and rates of transitions to reproductive states. Food supplementation increased survival, transitions to reproductive states, and abundance, but was not sufficient to prevent post-fire declines in any of these parameters. Mammalian predator exclusion did not strongly affect any of the considered parameters. Our results show that fire strongly influenced cotton rat populations in our study site, primarily by reducing cover and increasing predation risk from non-mammalian predators.

Survival, Mortality, and Predators of Red Tree Voles (Arborimus longicaudus)

Abstract Although estimations of vital rates are important to understand population dynamics of small mammals, there is little information on survival rates and causes of mortality for many species. In 2002–2003, we estimated monthly and annual survival of 50 radiocollared red tree voles (Arborimus longicaudus) during a study of movements and diel activity patterns in western Oregon. Estimated annual survival for both sexes combined was 0.15 (95% CI = 0.06 to 0.31) and was influenced little by mass at initial capture. In the analysis of explanatory variables, we did not find strong effects of gender, vole age, or forest age on survival. We suspect this may have been due to small sample size and low power to detect effects, because some of the point estimates were suggestive of large differences among groups. Most mortality was due to predation, with 15 of 25 deaths attributed to weasels (Mustela spp.). Weasels preyed upon significantly more females than males (14:1, respectively). Other confirmed or suspe...

Population dynamics of small mammal species in urbanized areas

Population dynamics of small mammals was monitored in urbanized forest ecosystems on a long-term basis. Urban rodent communities had higher densities due to a large proportion of hemisynanthropic species of Apodemus (Sylvemus) genus. It was found that small mammals displayed similar population dynamics in the park-forests in the same type of forest, but the pattern broke down in the city. Urban stress proved to have a stronger influence on the structure and population dynamics of small mammals than site conditions. Transformation of lower plant layers disturbs habitat of some species and creates favorable conditions for others. Increasing species richness and thickness of shrub layer make site conditions more favorable for the wood mouse and the field mouse—species that do not normally inhabit coniferous forests.

Inverse edge effect on nest predation in a Kenyan forest fragment: an experimental case study

Fragmentation of continuous habitat blocks into small, isolated patches may Cause gradual replacement of habitat specialists by generalists and edge-dwelling species, thereby altering trophic interactions within communities. When fragmentation progressively increases the edge-to-interior ratio of forest remnants, forest birds are typically exposed to higher levels of nest predation, especially so near forest edges. However, the strength and direction of this 'edge effect on nest predation' may vary with predator communities, which in turn call be affected by habitat type, landscape structure and geographical location. We studied avian nest predation in two isolated forest fragments in the Taita Hills of southeast Kenya, where small mammals, rather than birds, dominate predator communities. The use of artificial ground nests allowed us to reduce variation in laying date and microhabitat use, which are known to affect predation on natural nest in the study area. Predation rates did not increase near the forest boundary, but instead, were higher in the forest interior of one of the fragments. Such inverse edge effects may be caused by forest-dependent small mammals or snakes that can remove bird eggs. Although inverse edge effects may be more common in East African tropical forests than previously thought, and should therefore be taken into account when drafting conservation plans, the underlying mechanisms remain unclear. Further study of the population dynamics of small mammals and snakes, and their relative impact on nest predation in fragmented habitats, is therefore required.

Implications for Conservation of the Species Diversity and Population Dynamics of Small Mammals in an Isolated Reserve in Mexico City

ABSTRACT: We studied the influence of habitat loss and fragmentation in species diversity, population dynamics, and habitat use in a small mammal community in xeric palo loco (Senecio praecox) thickets at Reserva Ecologica del Pedregal de San Angel, a completely isolated nature reserve in Mexico City, Distrito Federal, from 1989 through 1990. It is a heterogeneous region, dominated by an old lava flow, with many boulders and crevices. Small mammals were captured using Sherman live traps in two 0.81-ha grids; each grid contained 10 rows and 10 columns, separated by 10 m. Nine species have disappeared since 1957 as a result of the loss of particular habitat such as grasslands, habitat fragmentation, and other causes. In our study, we recorded nine species; five species were exclusively recorded in the continuous native scrub of the reserve. Therefore, they are good indicators of the sites in the reserve that maintain the less perturbed habitats. Interestingly, no introduced rodents (i.e., roof rat (Rattus r...